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Exploring the Impact of Long-Term Evaporation on the Relationship Between Capillary Pressure and Water Saturation in Unsaturated Porous Media
Journal of Hydrology ( IF 6.4 ) Pub Date : 2020-03-01 , DOI: 10.1016/j.jhydrol.2020.124557
Aderonke O. Adegbule , Tohren C.G. Kibbey

Abstract The focus of this work was on understanding the impact of evaporation on the capillary pressure-saturation (Pc-S) state of a porous medium. Evaporation is ubiquitous near the ground surface in the vadose zone, but little is known about how evaporation impacts the relationship between capillary pressure and saturation. The hypothesis driving the work was that the Pc-S relationship is the result of an equilibrium between evaporative water loss, capillary forces, and the upward flow of water to replenish evaporated water. Experiments were conducted using two different porous media, a coarse sand and a nylon membrane with a 20 μm pore size. Long-term evaporation experiments were conducted using different configurations to control evaporation within the media. Results found that increased accessibility to evaporation caused saturation in drainage Pc-S curves to decrease over time, causing the curves to become closer to imbibition Pc-S curves. In the membrane, the high external surface area to pore volume ratio caused changes in evaporative flux to produce rapid changes in the Pc-S state of the medium. One implication of the work is that results suggest that long-term drainage experiments in vented columns may not necessarily provide a meaningful measurement of static Pc-S curve, but rather may be impacted by evaporation.

中文翻译:

探索长期蒸发对不饱和多孔介质中毛细管压力与水饱和度之间关系的影响

摘要 这项工作的重点是了解蒸发对多孔介质的毛细管压力饱和度 (Pc-S) 状态的影响。蒸发在包气带中的地表附近无处不在,但关于蒸发如何影响毛细管压力和饱和度之间的关系却知之甚少。推动这项工作的假设是,Pc-S 关系是蒸发失水、毛细管力和向上流动以补充蒸发水之间平衡的结果。使用两种不同的多孔介质进行实验,即粗砂和孔径为 20 μm 的尼龙膜。使用不同配置进行长期蒸发实验以控制介质内的蒸发。结果发现,增加蒸发可及性导致排水 Pc-S 曲线的饱和度随时间降低,导致曲线变得更接近渗吸 Pc-S 曲线。在膜中,高外表面积与孔体积比引起蒸发通量的变化,从而使介质的 Pc-S 状态发生快速变化。这项工作的一个含义是,结果表明,通风柱中的长期排水实验可能不一定提供对静态 Pc-S 曲线的有意义的测量,而是可能受到蒸发的影响。
更新日期:2020-03-01
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